Process for stabilizing liquids



Feb. 23, '1965 c. .1. wENDT, JR

PROCESS FOR STABILIZING LIQUIDS Filed March 15. 1961 223.50 mwN-55h United states Patent o 3,176,866 PRCESS FR STABILIZING MQUlDS Carl Il. Wendt, Jr., Los Angeles, Calif., assigner to The Ralph M. Parsons Company, Los Angeies, Calif., a corporation of Nevada Filed Mar. 13, 196i, Ser. No. 95,299- 1 Claim. (Cl. 20S-350) This invention is related to a process for stabilizing liquids and, more particularly, to a process for stabilizing liquids containing appreciable quantities of acidic gas constituents.

In processes involving multi-component liquids such as hydrocarbon condensates, crude oils, or partially refined liquids, it is' frequently necessary to stabilize the liquid by distilling olf low boiling point components in stabilizer columns. Where a liquid to be stabilized includes acidic gas constituents such as hydrogen suliide'or carbon dioxide, particularly in appreciable quantities, considerations of stabilizer' column size make it desirable that the build-up of large internal recycling of the low boiling point acidic gas constituents be avoided. Furthermore, the presence of these constituents in the overhead vapor product of a stabilizer column makes necessary the use of lower temperatures and/orhigher pressures in condensers used with such columns for condensation. of reiiux or overhead liquid product. In many instances, a requirement for a lower condenser temperature can be met only by external refrigerating systems because such lower temperatures are below the limits of plant cooling water. On the other hand, increased condenser pressures necessitate a higher reboiler temperature in the stabilizer column in order to maintain the reboiler boil-up rate.

Higher reboiler temperatures not only result in increased" cost for reboiler heat but frequently cannot even be utilized since the nature of the bottoms liquid is such that operations are conducted at the maximum allowable ternperature that avoids thermal cracking, including cracking of complex sulfur compounds with resultant production of additional hydrogen sulfide.

The process of the present invention removes acidic gas constituents from overhead vapor in stabilizer col-V umns, thereby promoting condensation of reflux or overhead liquid product and preventing `the build-up of the concentration of such constituents in the reflux. In addition, a gas product and/or an overhead liquid product are obtained from the overhead vapor, which products, upon being withdrawn, are substantially free of acidic gas constituents.

The process of the present invention for stabilizing liquids containing acidic gas constituents includes the step of heating such a liquid to produce an overhead vapor including acidic gas constituents. The overhead vapor is then contacted with an aqueous alkaline solution of a reagent that unites with acidic gases. The mixture of overhead vapor and alkaline solution is cooled and then separated to provide an alkaline solution rich in absorbed acidic gas constituents and a gas product substantially free of such constituents.

The aqueous solution is of an alkaline reagent which readily unitesl with weakly-acidic gases at comparatively low temperatures and which can be regenerated for reuse by heating. Such reagents have been previously proposed and used in many processes for the removal of acidic gases from hydrocarbon gases. Preferably, the alkanolamines,*particularly monoethanolamine, diethanolamine, or triethanolamine, are used in the practice of the present invention. However, other alkaline reagents such asthe alkali metal carbonatesand the alkali metal phosphates can also be used.

The practice of the process of the present invention 3,170,866 Patented Feb. 23, 1965 ICC effectively removes acidic gas constituents fromthe overhead vapor in a stabilizer column and, in stabillzer co1- Vumns where the principal object is to remove such constituents from the bottoms liquid, the practice of the process reduces the retlux ratio and, consequently, the column diameter for the same number of trays. Since it decreases the internal recycle, the practice of the process also reduces the necessary diameter of the stabilizer column, thereby achieving economies in initial cost of equipment. Furthermore, its practice results in savings in operating costs by permitting operation of the condenser in association with the stabilizer column at higher temperatures and/ or lower pressures than could bev effectively utilized without the practice of the process of` this invention. Also, when used in conjunction with an alkaline solution contacter to provide a linal alkaline solution wash, the process of thisY invention produces a gas product having ajhigh degree of purity without pressure reduction prior to such wash. As a consequence, the necessity for subsequent recompression of the gas product is eliminated and smaller capacity equipment may be used because of the small quantity of acidic gas constituents vin the productr entering the inal alkaline solution wash.

The details of the process of the present invention, as

reference to stabilization of a hydrocarbon condensate i containing acidic gas constituents. Furthermore, `it is described for convenience with reference to use of an amine solution. lt will be understood that the description of the process in this manner is not intended to limit its ap plicability to either hydrocarbon condensates or amine solutions.

A hydrocarbon condensate enters a stabilizer column lll through a feed line 12. The condensate is a multicomponent mixture of low-boiling, intermediate-boiling, and high-boiling hydrocarbon components together with an appreciable quantity of acidic gas constituents. The condensate ows to the bottom of the stabilizer column and is heated by circulation through a reboiler 14 within which it is partially vaporized. Steam to the reboiler is furnished through a line 16 and leaves as condensate by a line 18. The liquid remaining in the reboiler after vaporization leaves by a line 20 and passes to storage. Hot vapors from the reboiler are circulated through a line 22 into the bottom of the stabilizer column where they Y countercurrently heat the liquid llowing down the column.

Low boiling point and some intermediate boiling point hydrocarbon components, as well as the acidic gas con-` stituents of the condensate, are volatilized within the stabilizer and leave the top of the stabilizer as overhead vapor through a line 24. An aqueous amine solution entering by a line 26 is mixed with the overhead vapor and the mixture passes through a line 28 into a condenser 30. Water to cool the overhead product-amine mixture by indirect heat transfer enters the condenser by a line 32 and leaves by a line 34. Within the condenser, heavier components ofthe overhead product are condensed and substantially all of the acidic gas constituents in the overhead product vare absorbed in the amine solution. The cooled three-phase mixture leaves the condenser by a line 36 and passes into a reflux drum separator 38.

The reflux drum separator is a conventional separator for makinggas-'l-iquid and liquid-liquid separations. The gas phase, consisting of low boiling point hydrocarbon components substantially freeA of acidic gas constituents,

is separated from the liquid phase and leaves the separator by a line 40. The amine solution including absorbed acidic gas constituents is separated from condensed hydrocarbon components and leaves the separator by a line 42. Condensed hydrocarbon components leave the separator by a line 44 and are forced by a pump 46 Veither through a line 4S into the stabilizer column as reflux near its top, or through a line 50 to storage.

While not essential, a Water separator tray 52 is provided near the top of the stabilizer column below the point at which redux line 48 enters the column. The water separator tray recovers any amine carry-over from the rellux drum separator. Such amine carry-over passes through a line 54 to a Water separator drum 56. Hydrocarbon liquid separated in drum 56 is returned to the stabilizer column by a line 58 while recovered amine passes through a line 60 and is mixed in line 52 with rich amine solution leaving the reflux drum separator.

If the process of the present invention is used in a plant Vthat includes no other amine treating system, the rich amine solution from the separator is passed through a heat exchanger 62 and into a conventional regenerator 64. Optionally, the amine solution leaving the heat exchanger may be passed through a rich solution llash tank 66 before it enters the regenerator. Within heat exchanger 62, the rich amine solution is heated by passing in indirect heat transfer relationship with hot lean amine solution leaving the bottom of a regeneration column 64.`

Y il a 480 F. bottoms temperature and a 110 F. overhead condenser. The composition of the feed entering the column was approximately the following in mol percent:

The bottoms liquid product was 7,000 to 8,000 barrels per -day of 45 API stabilized crude containing less than The preheated rich amine solution, after being flashed to a lower pressure in lash tank 66, enters the upper portion of the regeneration column. The amine solution is reboiled with steam by means of a reboiler 63 to provide countercurrent stripping and to heat the amine solution, thereby liberating substantially all of the absorbed acidic gas constituents as Lthe solution llows downwardly through the stripper. Acidic gas constituents leave the top of the regeneration column through a line 70 and pass through a Water-cooled condenser 72 and a separator drum 74 in which condensed'liquids are separated from the acidicgas constituents. Condensed liquids are returned to the column through a line 76 while acidic gas constituents are removed through a line 78.

The hot lean amine solution is used to preheat rich amine solution in heat exchanger 62 as previously described. The cooled lean amine solution leaving the heat exchanger is passed through line 26 where it is mixed with overhead vapor from the stabilizer column as previously described. Y

If an amine system exists Within the plant in which the process of the present invention is used, lean amine solution can be withdrawn from the regenerated solution line of such `a system after the lean solution heat exchanger but before the lean solution cooler. The rich amine solution can be returned to the rich solution flash tank or the solution heat exchanger of the existing system.

The gas product leaving the rellux drum separator by line 40 is suiciently purified of acidic gas constituents so as to be used directly for plant fuel in most areas. When the amount of this product exceeds `the fuel requirements of the plant, or where it is desirable to further process it to purify it to meet gas pipeline specifications, the gas product may be treated in an amine contactor. However, the prior treatment by the process of the present invention greatly simplifie-s any further treatment of the gas because of the small quanti-ty of acidic gas constituents remaining in the gas product.

The following example will illustrate further the advantages of the process of the present invention.

Example l A stabilizer column was operated at 250 p.s.i.g. with (sov 0.1% by weight HZS. An aqueous solution containing 14% by weight monoethanolamine was injected into the overhead vapor line at a rate of 200 gallons per minute and absorbed about mols per hour of HZS and CO2 to make a substantially acidic gas-free overhead vapor product and rellux. Essentially complete separation of rich amine solution and hydrocarbon liquid was accomplished in the rellux drum separator. A water separator tray in the stabilizer and a water separator drum were installed ybut proved to be unnecessary.

For purposes of clarity, certain apparatus such as pumps, by-pass valves, expansion valves, surge tanks and the like have not been shown in the ilow sheet. The appropriate use of such equipment will be apparent to those skilled in the art, and the inclusion of such in the flow sheet is not necessary to provide an understanding of the process of thetpresent invention.

l claim:

A process for stabilizing multi-component hydrocarbon liquids containing acidic gas constituents, which process comprises the steps of (a) heating the hydrocarbon liquid in a column to produce an overhead vapor including hydrocarbon components and acidic gas constituents,

(b) contacting the overhead vapor with an aqueous solution of a reagent selected from the group consisting of alkanolamines, alkali metal carbonates, and alkali metal phosphates,

(c) cooling the overhead vapor-aqueous reagent solution to condense at `least part of the hydrocarbon components,

(d) separating a gas product and condensed hydrocarbon product, each substantially free of `acidic gas constituents, from the reagent solution rich in absorbed acidic gas constituents,

(e) returning at least part of the condensed hydrocarbon product as reflux to the column,

(f) regenerating the rich reagent solution by heating 4to remove absorbed acidic gas constituents, and

(g) contacting the overhead vapor with regenerated reagent solution.

References Cited in the tile of this patent UNITED STATES PATENTS 1,715,095 Morrell et al May 28, 1929 2,040,096 Miller May 12, 1936 2,621,216 White ec. 9, 1952 2,908,640 Dougherty Oct. 13, 1959 2,938,851 Stedman May 31, 1960 2,973,316 Howland Feb. 28, 1961 2,990,431V Cabbage June 27, 1961 

